The present invention relates to a fuel injector for internal combustion engines In a fuel filter described in U.S. Pat. No. 4,987,887, a piston-like valve member is axially displaceable in a guide bore of a valve body. The valve member has a conical valve sealing face on its lower end facing the combustion chamber with which it cooperates with a stationary valve seat face on the closed end of the guide bore. With the known a fuel injector, two injection orifices arranged downstream from the valve seat face opening from the closed end of the guide bore and opening into the combustion chamber of the internal combustion engine. Fuel flow to these injection orifices is controlled by the sealing cross section between the valve seat face and the valve sealing face. The valve member of the known fuel injector has two guide areas with which it is displaceably guided along the wall of the guide bore. A first upper guide area is provided on the end of the valve member which faces away from the combustion chamber and extends above a fuel pressure space that is formed by an enlargement in the cross section of the guide bore and opens into the one high-pressure fuel inlet channel. In addition to the function of secure guidance of the valve member, the upper guide area assumes the function of sealing the pressure space with respect to a spring space accommodating a valve spring acting on the valve member in the closing direction. In addition to this first upper guide area, the valve member has a second lower guide area in an area designed as a ring collar facing the combustion chamber with which the valve member cooperates with a reduced diameter of the guide bore. The lower guide area is designed as a ring collar, so that an annular clearance formed by the guide bore between the valve member and the wall of the guide bore starting from the pressure space is separated from a lower pressure space opening onto the valve seat face when the fuel injector is closed. During the upward opening motion of the valve member, the ring collar of the lower guide area of the valve member emerges from the overlap with the reduced diameter of the guide bore and thus opens an unthrottled flow cross section between the annular clearance and the lower pressure space.
To supply fuel to the lower pressure space, a throttle flow cross section is provided between the annular clearance and the lower pressure space through which fuel can flow into the lower pressure space when the fuel injector is closed, i.e., when the valve member is in contact with the valve seat. In the known fuel injector, this throttle cross section is provided as an annular throttle clearance between the ring collar of the lower guide area and the reduced diameter of the guide bore.
However, the disadvantage of this design of the connecting throttle cross section between the annular clearance and the lower pressure space in the known fuel injection valve for internal combustion engines is that it is difficult to set the correct throttle cross section reproducibly on various fuel injectors because of surface tolerances in the ring collar and in the wall of the guide bore. This method of producing a correct throttle gap is especially demanding with regard to manufacturing precision, which can thus be achieved only at great expense and great effort. However, a precise setting of the throttle cross section is extremely important from the standpoint of correct functioning of the fuel injector, in particular the pilot injection setting, so the possibility of setting the cross section on the basis of the annular throttle clearance between the guide collar and the wall of the guide bore is not sufficient.
The fuel injector for internal combustion engines Patent claim 1, has the advantage over the related art that the connecting throttle cross section between the annular clearance and the lower pressure space on the fuel injector can be established easily and reproducibly with a high precision. This is achieved through the design of the connecting throttle cross section according to the present invention as a throttle bore passing through the valve member at an oblique angle, the inlet orifice of the throttle bore being arranged in the area of the annular clearance, and the outlet orifice is arranged in the area of the lower pressure space.
Such a throttle bore can be produced with a high precision and simple means in terms of the manufacturing technology, and even a very small variation range in mass production can be further reduced. It is especially advantageous that contrary to the related art, such a throttle bore is not dependent upon any tolerance in the fit between the valve member and the geometry of the guide bore. The throttle bore in the valve member may have the same throttle cross section over its length, but it is also possible for the throttle cross section to be designed in two or more stages, in which case the smallest bore diameter determines the throttle flow cross section. This smallest throttle bore cross section may then be provided at the inlet of the throttle bore, in the middle area or at the outlet of the throttle bore (as shown in the embodiment). The design of the throttle bore as a two-stage or multi-stage bore has the advantage that good through flow can be achieved with a sufficient throttle effect, where the desired throttle effect can be achieved for each type of fuel injector with a simple construction on the basis of the diameter difference between the large throttle diameter and the smallest throttle diameter of the bore and the respective bore lengths between the larger part of the bore and the throttle cross section.
It is thus possible with the fuel injector according to the present invention to accurately and reproducibly adjust the throttle cross section between the annular clearance and the lower pressure space, which is important in shaping the injection pattern at the injector, with a simple construction.
Another advantage of the fuel injector according to the present invention is achieved due to the fact that an annular groove is provided at the transition between the ring collar forming the lower guide area and an adjacent area of the valve member which has a reduced cross section. This annular groove has the advantage that the lower edge of the ring collar which forms a control edge is machined so as to have a sharper edge, so that precise control can be achieved in the interaction with the corresponding collar of the guide bore.
Another advantage of the fuel injector according to the present invention is achieved by providing recesses on the valve member in the area of the lower pressure space, these recesses, preferably designed as polished sections, permitting a better unhindered flow from the annular clearance into the lower pressure space after the ring collar emerges from the bore shoulder face, so that the fuel which is under a high pressure can flow over out of the fuel inlet channel to the injection orifices as uniformly as possible through the annular clearance and the lower pressure space.